1. Field of the Invention
The present invention relates to an electrical connector, and more particularly to a land grid array (LGA) connector for electrically connecting an electronic package such as an LGA chip and a circuit substrate such as a printed circuit board (PCB).
2. Description of the Prior Art
Land grid array (LGA) electrical connectors are widely used in the connector industry for electrically connecting LGA chips to printed circuit boards (PCBs) in personal computers (PCs). Conventionally, one kind of the LGA connector mainly comprises an insulative housing, a multiplicity of contacts received therein, a metallic stiffener partly covering and reinforcing the housing, and a metal clip and a cam lever pivotably mounting on two opposite sides of the stiffener. The housing defines a multiplicity of terminal passageways in a rectangular array, for interferentially receiving corresponding terminals. Due to the very high density of the terminal array that an LGA chip may have, the LGA chip needs to be precisely seated on the LGA connector. This is to ensure reliable signal transmission between the terminals and the LGA chip.
Referring to FIGS. 5–7, such a conventional LGA connector 8 typically comprises an insulative housing 80, a plurality of electrical contacts 81 received in corresponding passageways (not labeled) of the housing 80, a metal stiffener 82 partly covering and reinforcing the housing 80, a cam lever 84 pivotably received in a front end 820 of the stiffener 82, and a metal clip 83 pivotably mounted to an opposite rear end 821 of the stiffener 82 for engaging with the cam lever 84. The housing 80 defines four sidewalls (not labeled) and a central cavity disposed between the sidewalls. The central cavity is used for receiving a land grid array (LGA) chip (not shown) therein. Each contact 81 has a contact portion protruding outwardly from an upper surface of the housing 80, for electrically connecting with a corresponding metal contact pad of the LGA chip that is received in the LGA connector 8, and a solder portion mounted on a printed circuit board (PCB) 9 (see FIG. 7) via a surface mounted solder ball 85 (see FIG. 7). The clip 83 comprises two opposite sides 830. A pair of pressing portions 831 is provided in respective middle portions of the sides 830, for pressing the LGA chip engaging with the terminals 81.
When the LGA connector 8 is electrically connected the PCB 9 and the LGA chip, firstly curing the solder ball 85 at high temperature in a convention cabinet using infrared radiant heaters, heat air can flow through the passageways to a bottom portion of the housing 80 to make the adhesive film of the contacts 81 activated quickly. The solder balls 85 of the contacts 81 melt and connect the corresponding contact pads attached on an upper surface of the PCB 9 so that the LGA connector 8 is electrically connected with the PCB 9. After cooled and frozen, the contacts 81 of the connector 8 is reliably and electrically soldered onto the PCB 9. Secondly, engaging the LGA chip with the LGA connector 8, the clip 83 is rotated upward. The LGA chip is placed in the central cavity of the housing 80. The clip 83 is rotated from a vertical portion to a horizontal portion to make the two opposite sides 830 of the clip 83 attach on corresponding sides of the LGA chip. The cam lever 84 is rotated to drive the clip 83 to gradually approach the housing 80 until the pressing portions 831 of the clip 83 press the LGA chip downwardly to make the contact pads of the LGA chip contact with the contact portions of the terminals 81 and make the LGA chip received in the central cavity therein. As a result, mechanical and electrical engagement between the LGA chip and the PCB 9 via the LGA connector 8 is attained.
However, it is desirable to solder some other electrical elements on a bottom surface of the PCB 9 after the LGA connector 8 is soldered on the upper surface of the PCB 9, so the PCB must be turned over and subjected to a reflow process with the LGA connector 8 already in place. In the reflow process, the solder balls 85 will melt again so that the LGA connector 8 connects with the PCB 9 only via an exterior tensility of the activated solder balls 85. Thus the LGA connector 8 will tend to incline downwardly because the center of gravity of the LGA connector 8 is near to the front end 820 of the stiffener 82. The solder balls 85 adjacent to the front end 820 may become disconnected from the contact pads of the PCB 9. When this happens, electrical engagement between some of the contacts 81 and the corresponding contact pads of the PCB 9 may be flawed. The LGA connector 8 may not reliably electrically connect with the PCB 9.
Thus, there is a need to provide a new LGA connector that overcomes the above-mentioned problems.